PSI Pharmaceutical Sciences 3 — Questions and Answers
Question 1: Which cytochrome P450 enzyme is responsible for the metabolism of the largest number of drugs?
- CYP3A4 (Correct answer)
- CYP2D6
- CYP2C9
- CYP1A2
Correct answer: CYP3A4
CYP3A4 is the most abundant hepatic CYP enzyme and metabolises approximately 50% of all drugs. It is subject to many important drug interactions.
Question 2: Renal clearance of a drug is increased when the drug is:
- Ionised at urinary pH (Correct answer)
- Highly protein bound
- Lipophilic
- Metabolised to inactive metabolites
Correct answer: Ionised at urinary pH
Ionised drugs cannot readily be reabsorbed through tubular epithelium, so they remain in urine and are excreted. Manipulating urinary pH to increase ionisation is used in poisoning management.
Question 3: Which dosage form is designed to release drug in the small intestine rather than the stomach?
- Enteric-coated tablet (Correct answer)
- Sublingual tablet
- Buccal film
- Effervescent tablet
Correct answer: Enteric-coated tablet
Enteric coatings (e.g., HPMC phthalate) resist acidic gastric pH but dissolve at the higher pH of the small intestine, protecting acid-labile drugs or preventing gastric irritation.
Question 4: Steady-state plasma concentration is reached after approximately how many half-lives of continuous dosing?
- 5 half-lives (Correct answer)
- 1 half-life
- 2 half-lives
- 10 half-lives
Correct answer: 5 half-lives
With repeated dosing, drug accumulates until input equals output. Steady state is effectively reached after 4–5 half-lives, when ~97% of the final plateau concentration is achieved.
Question 5: Which type of isomerism involves non-superimposable mirror image molecules?
- Enantiomerism (Correct answer)
- Diastereomerism
- Geometric isomerism
- Structural isomerism
Correct answer: Enantiomerism
Enantiomers are mirror images that cannot be superimposed. They have identical physical properties but can differ in pharmacological activity, toxicity and metabolism.
Question 6: An isotonic solution has the same osmolarity as:
- Blood plasma (~285–310 mOsm/kg) (Correct answer)
- Distilled water
- Normal saline only
- 5% glucose only
Correct answer: Blood plasma (~285–310 mOsm/kg)
Isotonic solutions match the osmolarity of blood plasma (~285–310 mOsm/kg), preventing osmotic shift across cell membranes. Both normal saline (0.9%) and 5% glucose are isotonic examples.
PSI Pharmaceutical Sciences 3
Which cytochrome P450 enzyme is responsible for the metabolism of the largest number of drugs?